1, 3-butadiene separating material, and separation method using said separating material

ABSTRACT

A separating material superior to conventional separating materials, and a separation method are provided, with which 1,3-butadiene is selectively separated and recovered from a mixed gas including 1,3-butadiene and C4 hydrocarbons other than 1,3-butadiene. A metal complex, which comprises a dicarboxylic acid compound (I) (see (I) below) represented by general formula (I), an ion of a metal such as beryllium, and a bipyridyl compound (II) represented by general formula (II), namely L-Z-L (II) (see (L) below), is characterized by including, as the dicarboxylic acid compound (I), at least two different dicarboxylic acid compounds (I). The metal complex is used as a 1,3-butadiene separating material. Formula (I) L is represented by any of the compounds below. Formula (L).

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No.PCT/JP2014/067521, filed on Jul. 1, 2014 (which claims priority fromJapanese Patent Application No. 2013-155625, filed on Jul. 26, 2013),the contents of which are incorporated herein by reference in theirentirety.

TECHNICAL FIELD

The present invention relates to a 1,3-butadiene separating materialcontaining a specific metal complex, and a method for separating1,3-butadiene from a mixed gas using that separating material.

BACKGROUND ART

Technologies are known for separating and recovering a targethydrocarbon gas (such as 1,3-butadiene) from a mixed gas containinghydrocarbons.

1,3-butadiene is an example of a hydrocarbon gas that is targeted forseparation and recovery. 1,3-butadiene is a compound that is useful as astarting material for the production of synthetic rubber as well as anintermediate of an extremely large number of compounds. 1,3-butadiene istypically produced by thermal decomposition of naphtha ordehydrogenation of butene. In these production methods, 1,3-butadiene isobtained in the form of one component of a mixed gas. Thus, it isnecessary to selectively separate and recover 1,3-butadiene from thismixed gas. Examples of main components in the mixed gas having fourcarbon atoms include 1,3-butadiene, isobutene, 1-butene, trans-2-butene,cis-2-butene, n-butane and isobutane. Since these compounds have thesame number of carbon atoms and similar boiling points, they aredifficult to separate from each other using industrial distillationmethods.

Another example of a separation method is extractive distillation. Sincethis method is an absorption method that uses a polar solvent, such asDMF, an extremely large amount of energy is required when recovering1,3-butadiene from the polar solvent. Thus, an adsorption method toseparate and recover 1,3-butadiene using less energy is desired.

However, since conventional porous materials (Patent Document 1) exhibitlow separation performance with respect to the target gas, multi-stepseparation is required, thereby leading to unavoidable increases in sizeof the separation apparatus.

Porous metal complexes that induce a dynamic structural change by anexternal stimulus have been developed as adsorbents that provideseparation performance superior to that of conventional porous materials(Non-Patent Document 1 and Non-Patent Document 2). In the case of usingthe porous materials described in these publications as gas adsorbents,a unique phenomenon has been observed in which, although gas is notadsorbed below a certain pressure, gas begins to be adsorbed once thatpressure is exceeded. In addition, a phenomenon has been observed inwhich the gate-opening pressure varies depending on the type of gas.

In the case of applying this porous material to an adsorbent in apressure swing adsorption system, gas can be separated extremelyefficiently. In addition, the range of pressure swing can be narrowed,thereby contributing to energy savings. Moreover, this can contribute todownsize and cost-reduction of the gas separation apparatus, enabling toenhance cost competitiveness for both high-purity gas products andfinished products made from the high-purity gases.

However, to meet growing demands for even greater cost reductions, it isnecessary to further improve adsorption and separation performance.

A metal complex [Zn(R-ip)(bpe)](wherein R represents H, Me, NO₂ or I)has been disclosed and the complex is composed of a zinc ion, varioustypes of isophthalic acid derivatives and 1,2-di(4-pyridyl)ethylene(Patent Document 2 and Non-Patent Document 3). However, although thesedisclosures contain discussions of the adsorption and separationcharacteristics relating to hydrocarbons having two carbon atoms, thereis no discussion regarding the adsorption and separation characteristicsof hydrocarbon gases having four carbon atoms, including 1,3-butadiene.

Attempts to change gate-opening pressure by mixing a plurality ofligands have been disclosed with respect to metal complexes consistingof a zinc ion, various types of isophthalic acid derivatives and4,4′-bipyridyl (Patent Document 3 and Non-Patent Document 4). However,these disclosures do not discuss the 1,3-butadiene separationcharacteristics of metal complexes composed of bidentate organic ligandsother than 4,4′-bipyridyl.

PRIOR ART DOCUMENTS Patent Documents

[Patent Document 1] Japanese Unexamined Patent Publication No. S51-43702

[Patent Document 2] Japanese Unexamined Patent Publication No.2011-068631

[Patent Document 3] Japanese Unexamined Patent Publication No.2012-031161

Non-Patent Documents

[Non-Patent Document 1] Kazuhiro Uemura and Susumu Kitagawa, FutureMaterials, Vol. 2, pp. 44-51 (2002)

[Non-Patent Document 2] Ryotaro Matsuda and Susumu Kitagawa, Petrotech,Vol. 26, pp. 97-104 (2003)

[Non-Patent Document 3] Satoshi Horike, Keisuke Kishida, YoshihiroWatanabe, Yasutaka Inubushi, Daiki Umeyama, Masayuki Sugimoto, TomohiroFukushima, Munehiro Inukai and Susumu Kitagawa, Journal of AmericanChemical Society, Vol. 134, pp. 9852-9855 (2012)

[Non-Patent Document 4] Satoshi Horike, Yasutaka Inubushi, Takashi Hori,Tomohiro Fukushima and Susumu Kitagawa, Chemical Science, Vol. 3, pp.116-120 (2012)

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

An object of the present invention is to provide a separating materialand separation method that are superior to the prior art in that theyare capable of selectively separating and recovering 1,3-butadiene froma mixed gas containing 1,3-butadiene and hydrocarbons having four carbonatoms other than 1,3-butadiene.

Means for Solving the Problems

As a result of extensive studies, the inventors of the present inventionhave found that the aforementioned object can be achieved in the case ofusing a separating material containing a metal complex composed of ametal ion, a dicarboxylic acid compound (I) and a dipyridyl compound(II), wherein the dicarboxylic acid compound (I) is composed of two ormore types of dicarboxylic acid compounds (I), thereby leading tocompletion of the present invention. Namely, the present inventionrelates to [1] to [14] indicated below.

[1] A 1,3-butadiene separating material that selectively adsorbs1,3-butadiene from a mixed gas containing 1,3-butadiene and ahydrocarbon having four carbon atoms other than 1,3-butadiene,comprising a metal complex consisting of:

a dicarboxylic acid compound (I) represented by the following generalformula (I):

wherein X represents a carbon atom or nitrogen atom, Y represents ahydrogen atom, optionally substituted alkyl group having 1 to 4 carbonatoms, alkenyl group having 2 to 4 carbon atoms, alkoxy group having 1to 4 carbon atoms, formyl group, acyloxy group having 2 to 4 carbonatoms, hydroxyl group, alkoxycarbonyl group having 2 to 4 carbon atoms,nitro group, cyano group, amino group, monoalkylamino group having 1 to4 carbon atoms, dialkylamino group having 2 to 4 carbon atoms, acylaminogroup having 2 to 4 carbon atoms, sulfo group, sulfonate group, carboxylgroup or halogen atom in the case X represents a carbon atom or Y is notpresent in the case X represents a nitrogen atom, and R¹, R² and R³respectively and independently represent a hydrogen atom, optionallysubstituted alkyl group having 1 to 4 carbon atoms or halogen atom;

an ion of at least one type of metal selected from the group consistingof beryllium, magnesium, calcium, strontium, barium, titanium, vanadium,chromium, manganese, iron, ruthenium, cobalt, rhodium, nickel,palladium, platinum, copper, zinc and cadmium; and,

a dipyridyl compound (II) represented by the following general formula(II):L-Z-L  (II)

wherein L is represented by any of the following formulas:

wherein R⁴, R⁵, R⁶ and R⁷ respectively and independently represent ahydrogen atom, alkyl group having 1 to 4 carbon atoms or a halogen atom,and Z represents —CR⁸R⁹—CR¹⁰R¹¹— (wherein R⁸, R⁹, R¹⁰ and R¹¹respectively and independently represent a hydrogen atom, alkyl grouphaving 1 to 4 carbon atoms, hydroxyl group or halogen atom), an alkylenegroup having 3 to 4 carbon atoms, —CH═CH—, —C≡C—, —S—S—, —N═N—, —O—CH₂—,—NH—CH₂— or —NHCO—); wherein

two or more different types of the dicarboxylic acid compound (I) arecontained as the dicarboxylic acid compound (I).

[2] The 1,3-butadiene separating material described in [1], wherein thedicarboxylic acid compound (I) comprises two or more dicarboxylic acidsselected from the group consisting of isophthalic acid,5-methylisophthalic acid, 5-tert-butylisophthalic acid,5-methoxyisophthalic acid, 5-nitroisophthalic acid, sodium5-sulfoisophthalate, lithium 5-sulfoisophthalate and trimesic acid.

[3] The 1,3-butadiene separating material described in [1] or [2],wherein a combination of the dicarboxylic acid compounds (I) is5-nitroisophthalic acid and sodium 5-sulfoisophthalate,5-nitroisophthalic acid and lithium 5-sulfoisophthalate, or5-nitroisophthalic acid and 5-tert-butylisophthalic acid.

[4] The 1,3-butadiene separating material described in any of [1] to[3], wherein the dipyridyl compound (II) is at least one selected fromthe group consisting of 1,2-di(4-pyridiyl)ethylene,1,2-di(4-pyridyl)ethane, 4,4′-azobispyridine and 4,4′-dipyridyldisulfide.

[5] The 1,3-butadiene separating material described in any of [1] to[4], wherein the metal ion is at least one selected from the groupconsisting of a cobalt ion, nickel ion and zinc ion.

[6] The 1,3-butadiene separating material described in any of [1] to[5], wherein the metal complex has a structure that is a triplyinterpenetrating pseudo-diamondoid framework.

[7] The 1,3-butadiene separating material described in any of [1] to[6], wherein the hydrocarbon having four carbon atoms other than1,3-butadiene is at least one selected from the group consisting of1-butene, isobutene, trans-2-butene, cis-2-butene, isobutane andn-butane.

[8] A 1,3-butadiene separation method comprising: an adsorption step forcontacting a separating material with a mixed gas containing1,3-butadiene and a hydrocarbon having four carbon atoms other than1,3-butadiene and selectively adsorbing 1,3-butadiene onto theseparating material, followed by a regeneration step for desorbing the1,3-butadiene adsorbed onto the separating material from the separatingmaterial and capturing the released 1,3-butadiene, wherein theseparating material is the separating material described in any of [1]to [7].

[9] The 1,3-butadiene separation method described in [8], wherein theseparation method is pressure swing adsorption.

[10] The 1,3-butadiene separation method described in [8], wherein theseparation method is temperature swing adsorption.

[11] A separation membrane comprising a porous support and the1,3-butadiene separating material described in any of [1] to [7]attached to the surface of the porous support.

[12] A separation membrane comprising a polymeric material and the1,3-butadiene separating material described in any of [1] to [7] kneadedand dispersed in the polymeric material.

[13] A 1,3-butadiene separation method, comprising: contacting a mixedgas containing 1,3-butadiene and a hydrocarbon having four carbon atomsother than 1,3-butadiene with a separation membrane and selectivelyallowing the 1,3-butadiene to pass through the separation membrane toobtain a gas having a higher 1,3-butadiene concentration than the mixedgas, wherein the separation membrane is the separation membranedescribed in [11] or [12].

[14] A method for producing the metal complex described in [1],comprising reacting a salt of at least one type of metal selected fromthe group consisting of beryllium, magnesium, calcium, strontium,barium, titanium, vanadium, chromium, manganese, iron, ruthenium,cobalt, rhodium, nickel, palladium, platinum, copper, zinc and cadmium,two or more types of the dicarboxylic acid compound (I), and thedipyridyl compound (II) and precipitating a metal complex, wherein wetgrinding is carried out during the reaction.

Effects of the Invention

According to the present invention, 1,3-butadiene can be separated andrecovered from a mixed gas containing 1,3-butadiene at a higher level ofseparation performance than that of the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing the structure of apseudo-diamondoid framework.

FIG. 2 is a schematic diagram showing the three-dimensional structure ofa triply interpenetrating pseudo-diamondoid framework.

FIG. 3 is a schematic diagram of an apparatus for recovering1,3-butadiene from a mixed gas by pressure swing adsorption.

FIG. 4 is an adsorption isotherm of the metal complexes of Examples 1 to3 and Comparative Example 1 with respect to 1,3-butadiene at 25° C.

FIG. 5 is an adsorption isotherm of the metal complexes of Examples 4and 5 and Comparative Example 1 with respect to 1,3-butadiene at 25° C.

FIG. 6 is a time profile of the amounts of 1,3-butadiene adsorbed to themetal complexes of Examples 6 to 9 and Comparative Example 1 at 25° C.

FIG. 7 is an adsorption-desorption isotherm of 1,3-butadiene andtrans-2-butene in the metal complex of Example 2 at 25° C.

FIG. 8 is an adsorption-desorption isotherm of 1,3-butadiene andtrans-2-butene in the separating material of Comparative Example 2 inthe form of zeolite at 25° C.

MODE FOR CARRYING OUT THE INVENTION

<1,3-Butadiene Separating Material>

The 1,3-butadiene separating material of the present invention comprisesa metal complex composed of a dicarboxylic acid compound (I), a specificmetal ion, and a dipyridyl compound (II) capable of bidentatecoordination with the metal ion, wherein the dicarboxylic acid compound(I) comprises two or more different types of the dicarboxylic acidcompound (I). The 1,3-butadiene separating material of the presentinvention can be used to selectively separate 1,3-butadiene from, forexample, a mixed gas containing 1,3-butadiene and hydrocarbons havingfour carbon atoms other than 1,3-butadiene. The hydrocarbon having fourcarbon atoms other than 1,3-butadiene can be at least one selected fromthe group consisting of 1-butene, isobutene, trans-2-butene,cis-2-butene, isobutane and n-butane.

<Metal Complex>

The metal complex used in the present invention can be produced byreacting two or more types of the dicarboxylic acid compound (I), a saltof at least one type of metal selected from the group consisting ofberyllium, magnesium, calcium, strontium, barium, titanium, vanadium,chromium, manganese, iron, ruthenium, cobalt, rhodium, nickel,palladium, platinum, copper, zinc and cadmium, and a dipyridyl compound(II), capable of bidentate coordination with the metal ion, for severalminutes to several days in a solvent, and precipitating crystals.

<Dicarboxylic Acid Compound (I)>

The dicarboxylic acid compound (I) used in the present invention isrepresented by the following general formula (I):

wherein X represents a carbon atom or nitrogen atom, Y represents ahydrogen atom, optionally substituted alkyl group having 1 to 4 carbonatoms, alkenyl group having 2 to 4 carbon atoms, alkoxy group having 1to 4 carbon atoms, formyl group, acyloxy group having 2 to 4 carbonatoms, hydroxyl group, alkoxycarbonyl group having 2 to 4 carbon atoms,nitro group, cyano group, amino group, monoalkylamino group having 1 to4 carbon atoms, dialkylamino group having 2 to 4 carbon atoms, acylaminogroup having 2 to 4 carbon atoms, sulfo group, sulfonate group, carboxylgroup or halogen atom in the case X represents a carbon atom, or Y isnot present in the case X represents a nitrogen atom, and R¹, R² and R³respectively and independently represent a hydrogen atom, optionallysubstituted alkyl group having 1 to 4 carbon atoms or halogen atom.

X in general formula (I) is a carbon atom or nitrogen atom. Y is notpresent in the case X is a nitrogen atom.

In the case X is a carbon atom, Y is a hydrogen atom, optionallysubstituted alkyl group having 1 to 4 carbon atoms, alkenyl group having2 to 4 carbon atoms, alkoxy group having 1 to 4 carbon atoms, formylgroup, acyloxy group having 2 to 4 carbon atoms, hydroxyl group,alkoxycarbonyl group having 2 to 4 carbon atoms, nitro group, cyanogroup, amino group, monoalkylamino group having 1 to 4 carbon atoms,dialkylamino group having 2 to 4 carbon atoms, acylamino group having 2to 4 carbon atoms, sulfo (—SO₃H) group, sulfonate group (such as—SO₃Na), carboxyl group or halogen atom.

Examples of alkyl groups having 1 to 4 carbon atoms include linear orbranched alkyl groups, such as a methyl group, ethyl group, n-propylgroup, isopropyl group, n-butyl group, isobutyl group or tert-butylgroup.

Examples of optional substituents of the alkyl groups include alkoxygroups (such as a methoxy group, ethoxy group, n-propoxy group,isopropoxy group, n-butoxy group, isobutoxy group or tert-butoxy group),amino groups, monoalkylamino groups (such as a methylamino group),dialkylamino groups (such as a dimethylamino group), formyl group, epoxygroups, acyloxy groups (such as an acetoxy group, n-propanoyloxy group,n-butanoyloxy group, pivaloyloxy group or benzoyloxy group),alkoxycarbonyl groups (such as a methoxycarbonyl group, ethoxycarbonylgroup or n-butoxycarbonyl group), and carboxylic anhydride groups (suchas a —CO—O—CO—R group, wherein R represents an alkyl group having 1 to 4carbon atoms). In the case an alkyl group has a substituent, the numberof substituents is preferably 1 to 3 and more preferably 1.

Examples of alkenyl groups having 2 to 4 carbon atoms include a vinylgroup, allyl group, 1-propenyl group and butenyl group.

Examples of alkoxy groups having 1 to 4 carbon atoms include a methoxygroup, ethoxy group, n-propoxy group, isopropoxy group, n-butoxy group,isobutoxy group and tert-butoxy group.

Examples of acyloxy groups having 2 to 4 carbon atoms include an acetoxygroup, n-propanoyloxy group, n-butanoyloxy group, pivaloyloxy group andbenzoyloxy group.

Examples of alkoxycarbonyl groups having 2 to 4 carbon atoms include amethoxycarbonyl group, ethoxycarbonyl group and n-butoxycarbonyl group.

Examples of monoalkylamino groups having 1 to 4 carbon atoms include amethylamino group. Examples of dialkylamino groups having 2 to 4 carbonatoms include a dimethylamino group. Examples of acylamino groups having2 to 4 carbon atoms include an acetylamino group.

Examples of halogen atoms include fluorine, chlorine, bromine andiodine.

Examples of sulfonate groups include a lithium sulfonate group, sodiumsulfonate group and potassium sulfonate group.

R¹, R² and R³ in general formula (I) respectively and independentlyrepresent a hydrogen atom, optionally substituted alkyl group having 1to 4 carbon atoms or halogen atom. R¹, R² and R³ may be the same ordifferent.

Examples of alkyl groups having 1 to 4 carbon atoms represented by R¹,R² and R³ include linear or branched alkyl groups, such as a methylgroup, ethyl group, n-propyl group, isopropyl group, n-butyl group,isobutyl group or tert-butyl group.

Examples of optional substituents of the alkyl groups include alkoxygroups (such as a methoxy group, ethoxy group, n-propoxy group,isopropoxy group, n-butoxy group, isobutoxy group or tert-butoxy group),amino groups, monoalkylamino groups (such as a methylamino group),dialkylamino groups (such as a dimethylamino group), formyl group, epoxygroups, acyloxy groups (such as an acetoxy group, n-propanoyloxy group,n-butanoyloxy group, pivaloyloxy group or benzoyloxy group),alkoxycarbonyl groups (such as a methoxycarbonyl group, ethoxycarbonylgroup or n-butoxycarbonyl group), and carboxylic anhydride groups (suchas a —CO—O—CO—R group, wherein R represents an alkyl group having 1 to 4carbon atoms). In the case an alkyl group has a substituent, the numberof substituents is preferably 1 to 3 and more preferably 1.

Examples of halogen atoms include fluorine, chlorine, bromine andiodine.

In the case X is a nitrogen atom, an example of the dicarboxylic acidcompound (I) is 3,5-pyridinedicarboxylic acid.

From the viewpoint of the ease of adopting a pseudo-diamondoidstructure, it is preferable that R¹, R² and R³ respectively andindependently represent a hydrogen atom, alkyl group having 1 to 4carbon atoms or halogen atom. In the case X is a carbon atom, Y ispreferably a hydrogen atom, optionally substituted alkyl group having 1to 4 carbon atoms, alkoxy group having 1 to 4 carbon atoms, nitro group,carboxyl group or sulfonate group. The optionally substituted alkylgroup having 1 to 4 carbon atoms is preferably a methyl group ortert-butyl group. The alkoxy group having 1 to 4 carbon atoms ispreferably a methoxy group.

The dicarboxylic acid compound (I) is preferably a dicarboxylic acid inwhich R¹, R² and R³ are hydrogen atoms, X is a carbon atoms, and Y isany of a hydrogen atom, methyl group, tert-butyl group, methoxy group,nitro group, sulfonate group or carboxyl group. More specifically,isophthalic acid, 5-methylisophthalic acid, 5-tert-butylisophthalicacid, 5-methoxyisophthalic acid, 5-nitroisophthalic acid, sodium5-sulfoisophthalate, lithium 5-sulfoisophthalate, and trimesic acid arepreferable, isophthalic acid, 5-methylisophthalic acid and5-nitroisophthalic acid are more preferable, and from the viewpoint ofseparation performance, 5-nitroisophthalic acid is most preferable.

The present invention is characterized by combining two or more types ofthe dicarboxylic acid compound (I) to compose a metal complex. As aresult of combining two or more types of the dicarboxylic acid compound(I), there is the effect of increasing the recovery efficiency of1,3-butadiene since the gate-opening pressure of 1,3-butadiene is lowerin comparison with a metal complex composed from only one type of thedicarboxylic acid compound (I).

Preferable combinations of the dicarboxylic acid compound (I) include5-nitroisophthalic acid and isophthalic acid, 5-nitroisophthalic acidand 5-methylisophthalic acid, 5-nitroisophthalic acid and sodium5-sulfoisophthalate, 5-nitroisophthalic acid and lithium5-sulfoisophthalate, 5-nitroisophthalic acid and 5-tert-butylisophthalicacid, 5-nitroisophthalic acid and 3,5-pyridinedicarboxylic acid, and5-nitroisophthalic acid and trimesic acid. Moreover, from the viewpointof adsorption performance, the combinations of 5-nitroisophthalic acidand sodium 5-sulfoisophthalate, 5-nitroisophthalic acid and lithium5-sulfoisophthalate, and 5-nitroisophthalic acid and5-tert-butylisophthalic acid are more preferable, and the combination of5-nitroisophthalic acid and 5-tert-butylisophthalic acid is even morepreferable.

Among the two or more types of the dicarboxylic acid compound (I), theamount of the dicarboxylic acid compound (I) serving as base ispreferably 70 mol % to 95 mol %, and more preferably 80 mol % to 90 mol%, based on the total amount (number of moles) of the dicarboxylic acidcompound (I).

In the case the dicarboxylic acid compound (I) serving as base is5-nitroisophthalic acid, the preferable ratio of other dicarboxylic acidcompounds (I) complies with that indicated above.

The ratio between 5-nitroisophthalic acid and 5-sulfoisophthalate issuch that the ratio of 5-sulfoisophthalate to the total amount (numberof moles) of the dicarboxylic acid compound (I) is preferably 5 mol % to30 mol %. From the viewpoint of adsorption performance, the ratio ismore preferably 10 mol % to 20 mol %.

The ratio between 5-nitroisophthalic acid and 5-tert-butylisophthalicacid is such that the ratio of 5-tert-butylisophthalic acid to the totalamount (number of moles) of the dicarboxylic acid compound (I) ispreferably 5 mol % to 30 mol %. From the viewpoint of adsorptionperformance, the ratio is more preferably 10 mol % to 20 mol %.

<Metal Ion>

The metal ion that composes the metal complex used in the separatingmaterial of the present invention is an ion of at least one type ofmetal selected from the group consisting of beryllium, magnesium,calcium, strontium, barium, titanium, vanadium, chromium, manganese,iron, ruthenium, cobalt, rhodium, nickel, palladium, platinum, copper,zinc and cadmium. Among these, a cobalt ion, nickel ion and zinc ion arepreferable from the viewpoint of complex formation, and a zinc ion ismore preferable.

A salt, hydroxide or oxide of the aforementioned metals can be used as ametal raw material when producing the metal complex of the presentinvention. Although a single metal raw material is preferably used forthe metal raw material, two or more types of metal raw materials mayalso be used after mixing. Examples of these metal salts that can beused include organic acid salts, such as acetates or formates, andinorganic acid salts, such as hydrochlorides, hydrobromides, sulfates,nitrates or carbonates. Among these, hydroxides and oxides arepreferable from the viewpoint of the formation of by-productsaccompanying the reaction, and oxides are more preferable.

<Dipyridyl Compound (II)>

The dipyridyl compound (II) used in the present invention is an organicligand capable of bidentate coordination with a metal ion, and isrepresented by the following general formula (II):L-Z-L  (II)

wherein L is represented by any of the following formulas:

wherein R⁴, R⁵, R⁶ and R⁷ respectively and independently represent ahydrogen atom, alkyl group having 1 to 4 carbon atoms or a halogen atom,and Z represents —CR⁸R⁹—CR¹⁰R¹¹— (wherein R³, R⁹, R¹⁰ and R¹¹respectively and independently represent a hydrogen atom, alkyl grouphaving 1 to 4 carbon atoms, hydroxyl group or halogen atom), an alkylenegroup having 3 to 4 carbon atoms, —CH═CH—, —C≡C—, —S—S—, —N═N—, —O—CH₂—,—NH—CH₂— or —NHCO—).

R⁴, R⁵, R⁶ and R⁷ that compose L respectively and independentlyrepresent a hydrogen atom, alkyl group having 1 to 4 carbon atoms orhalogen atom. Examples of alkyl groups having 1 to 4 carbon atoms andhalogen atoms are as explained with respect to the dicarboxylic acidcompound (I). R⁴, R⁵, R⁶ and R⁷ are preferably hydrogen atoms or alkylgroups having 1 to 4 carbon atoms in terms of the amount of gasadsorbed, and R⁴, R⁵, R⁶ and R⁷ are more preferably all hydrogen atoms.

Z represents —CR⁸—R⁹CR¹⁰R¹¹— (wherein R⁸, R⁹, R¹⁰ and R¹¹ respectivelyand independently represent a hydrogen atom, alkyl group having 1 to 4carbon atoms, hydroxyl group or halogen atom), an alkylene group having3 to 4 carbon atoms, —CH═CH—, —C≡C—, —S—S—, —N═N—, —O—CH₂—, —NH—CH₂— or—NHCO—. Examples of alkyl groups having 1 to 4 carbon atoms and halogenatoms are as explained with respect to the dicarboxylic acid compound(I). Examples of alkylene groups having 3 to 4 carbon atoms include a1,3-propylene group, 1,4-butylene group and 2-methyl-1,3-propylenegroup.

From the viewpoint of easily adopting a pseudo-diamondoid structure, Zis preferably —CR⁸R⁹—CR¹⁰R¹¹— (wherein R⁸, R⁹, R¹⁰ and R¹¹ respectivelyand independently represent a hydrogen atom, alkyl group having 1 to 4carbon atoms, hydroxyl group or halogen atom), an alkylene group having3 to 4 carbon atoms, —CH═CH—, —S—S— or —NHCO—. In particular, Z is morepreferably —CR⁸R⁹—CR¹⁰R¹¹— (wherein R⁸, R⁹, R¹⁰ and R¹¹ are all hydrogenatoms), —CR⁸R⁹—CR¹⁰R¹¹— (wherein R⁸ and R¹⁰ are hydrogen atoms and R⁹and R¹¹ are hydroxyl groups), a 1,3-propylene group, —CH═CH—, —S—S—,—N═N— or —NHCO—.

From the viewpoint of easily adopting a pseudo-diamondoid structure, thedipyridyl compound (II) is preferably 1,2-di(4-pyridyl)ethylene,1,2-di(4-pyridyl)ethane, 1,2-di(4-pyridyl)ethylene glycol,1,3-di(4-pyridyl)propane, 4,4′-azobispyridine, 4,4′-dipyridyl disulfideor N-(4-pyridyl)isonicotinamide, and more preferably1,2-di(4-pyridyl)ethylene, 1,2-di(4-pyridyl)ethane, 4,4′-azobispyridineor 4,4′-dipyridyl disulfide.

<Metal Complex Production Method>

The metal complex used in the separating material of the presentinvention can be produced by reacting two or more types of thedicarboxylic acid compound (I), a salt of at least one type of metalselected from the group consisting of beryllium, magnesium, calcium,strontium, barium, titanium, vanadium, chromium, manganese, iron,ruthenium, cobalt, rhodium, nickel, palladium, platinum, copper, zincand cadmium, and a dipyridyl compound capable of bidentate coordinationwith the metal ion for several minutes to several days in a solvent atnormal pressure, and precipitating crystals. For example, the metalcomplex of the present invention can be obtained by mixing and reactingan aqueous solution or water-containing organic solvent solution of theaforementioned metal salt and an organic solvent solution containing twoor more types of the dicarboxylic acid compound (I) and the dipyridylcompound (II) at normal pressure.

One example of the production method is a method that uses a wetgrinder. Two or more types of the dicarboxylic acid compound (I), metalsalt, the dipyridyl compound (II), solvent and grinding balls are placedin the apparatus followed by carrying out the reaction while carryingout a grinding procedure.

In the aforementioned reaction, it is preferable that the raw materialsbe reacted in the wet grinder and the reaction be completed whilegrinding the reaction product in the form of the metal complex thatprecipitates in the form of crystals. Examples of apparatuses used forwet grinding include pulverizers, such as a ball mill or rod mill, andmixers, such as a kneader. The use of a grinder is advantageous from theviewpoint of adsorption rate since a metal complex having a smallerparticle diameter can be obtained in comparison with conventionalhydrothermal synthesis methods and the like. In addition, productiontime can be shortened considerably since synthesis is completed inroughly several minutes to several hours.

The mixing ratio between the dicarboxylic acid compound (I) and thedipyridyl compound (II) when producing the metal complex is such thatthe ratio of the dicarboxylic acid compound (I) to the dipyridylcompound (II) is preferably within the range of a molar ratio of 1:5 to8:1 and more preferably within the range of a molar ratio of 1:3 to 6:1.Although the target metal complex can be obtained even if the reactionis carried out outside these ranges, yield decreases and side reactionsincrease, thereby making this undesirable. The aforementioned ratio ofthe dicarboxylic acid compound (I) is that based on the total amount oftwo or more types of the dicarboxylic acid compound (I), and thisapplies similarly hereinafter.

The mixing ratio between the metal salt and dipyridyl compound (II) whenproducing the metal complex is such that the ratio of the metal salt tothe dipyridyl compound (II) is preferably within the range of a molarratio of 3:1 to 1:3 and more preferably within the range of a molarratio of 2:1 to 1:2. In the case of a ratio outside these ranges, yieldof the metal complex decreases and unreacted raw materials remain,thereby making it difficult to purify the resulting metal complex.

The molar concentration of the dicarboxylic acid compound (I) in asolution for producing the metal complex is preferably 0.005 mol/L to5.0 mol/L and more preferably 0.01 mol/L to 2.0 mol/L. Although thetarget metal complex is obtained even if the reaction is carried out ata lower concentration than those indicated above, yield decreases,thereby making this undesirable. In addition, at a higher concentrationthan those indicated above, solubility decreases and the reaction maynot proceed smoothly.

The molar concentration of the metal salt in the solution for producingthe metal complex is preferably 0.005 mol/L to 5.0 mol/L and morepreferably 0.01 mol/L to 2.0 mol/L. Although the target metal complex isobtained even if the reaction is carried out at a lower concentrationthan those indicated above, yield decreases, thereby making thisundesirable. In addition, at a higher concentration than those indicatedabove, unreacted metal salt remains, thereby making it difficult topurify the resulting metal complex.

The molar concentration of the dipyridyl compound (II) in the solutionfor producing the metal complex is preferably 0.001 mol/L to 5.0 mol/Land more preferably 0.005 mol/L to 2.0 mol/L. Although the target metalcomplex is obtained even at a concentration lower than those indicatedabove, yield decreases, thereby making this undesirable. In addition, ata higher concentration than those indicated above, solubility decreasesand the reaction may not proceed smoothly.

<Solvent>

An organic solvent, water or a mixed solvent thereof can be used for thesolvent used to produce the metal complex. Specific examples of solventsthat can be used include methanol, ethanol, propanol, diethyl ether,dimethoxyethane, tetrahydrofuran, hexane, cyclohexane, heptane, benzene,toluene, methylene chloride, chloroform, acetone, ethyl acetate,acetonitrile, N,N-dimethylformamide, dimethylsulfoxide, water and mixedsolvents thereof. A mixed solvent consisting of 1% by weight to 80% byweight of water and an organic solvent is preferable as a mixed solvent.An aprotic polar solvent, such as tetrahydrofuran, acetone,acetonitrile, N,N-dimethylformamide, N,N-diethylformamide ordimethylsulfoxide is preferable for the organic solvent used in a mixedsolvent with water. Among these solvents, water alone or a mixed solventof N,N-dimethylformamide and water is particularly preferable. The pHmay be adjusted to a pH preferable for complex formation by adding anacid or base to the solvent.

The concentration of water in the mixed solvent is preferably 1% byweight to 80% by weight, more preferably 3% by weight to 60% by weight,and most preferably 5% by weight to 55% by weight from the viewpoint ofthe particle size of the metal complex formed.

The reaction temperature is preferably −20° C. to 150° C. and morepreferably 50° C. to 130° C. The reaction time is preferably 1 hour to24 hours and more preferably 2 hours to 10 hours. In the case of using awet grinder, the reaction temperature may be 10° C. to 30° C. Thereaction time can also be shortened to about 10 minutes to 2 hours.

Completion of the reaction can be confirmed by quantifying the residualamounts of raw materials by gas chromatography or high-performanceliquid chromatography. Following completion of the reaction, theresulting mixed liquid is subjected to vacuum filtration to collect theprecipitate followed by washing with an organic solvent andvacuum-drying for several hours at, for example, 60° C. to 100° C. toobtain the metal complex of the present invention. A highly crystallinemetal complex has high purity and delivers superior adsorptionperformance. The pH may be adjusted to a suitable pH using an acid orbase in order to enhance crystallinity.

<Structure of Metal Complex>

The metal complex of the present invention obtained in the mannerdescribed above has a three-dimensional structure that is a multiplyinterpenetrating pseudo-diamondoid framework formed by coordination ofthe carboxylate ions of two dicarboxylic acid compounds (I) and twodipyridyl compounds (II) per single metal ion. The structure of thepseudo-diamondoid framework is shown in FIG. 1, while a schematicdiagram of the three-dimensional structure of a triply interpenetratingpseudo-diamondoid framework is shown in FIG. 2. The metal complexpreferably has a structure that is a triply interpenetratingpseudo-diamondoid framework.

Although the metal complex used in the separating material of thepresent invention is normally composed such that the ratio of the metalion, dicarboxylic acid compound (I) and dipyridyl compound (II) is 1mole:1 mole:1 mole, deviation from the aforementioned ratio is permittedprovided the effects of the present invention are obtained.

In the present description, a “pseudo-diamondoid framework” is definedas a three-dimensional structure that resembles the structure of adiamond that is formed by coordination of carboxylate ions of twodicarboxylic acid compounds (I) and two dipyridyl compounds (II) persingle metal ion.

In the present description, a “structure that is a multiplyinterpenetrating pseudo-diamondoid framework” is defined as athree-dimensional structure in which a plurality of pseudo-diamondoidframeworks is interpenetrating in a form that fills in their mutualpores. Whether or not the metal complex “has a structure that is amultiply interpenetrating pseudo-diamondoid framework” can be confirmedby, for example, crystal X-ray structural analysis or powder X-raystructural analysis.

The three-dimensional structure of the metal complex of the presentinvention can be changed even after synthesis. Pore structure and sizealso change accompanying a change in the three-dimensional structure ofthe metal complex. This structural change is presumed to depend on suchfactors as the type of adsorbate, pressure and temperature. Namely, itis believed that the metal complex of the present invention exhibitshigh selectivity since the degree of structural change varies dependingon the adsorbates in addition to a difference in interaction between thepore surfaces and the adsorbate (the intensity of that interaction isproportional to the magnitude of the Lennard-Jones potential of thesubstance). Since the structure returns to its original structure afteran adsorbate has been desorbed, pore structure would also return to itsoriginal structure.

In the present invention, gate-opening pressure can be controlled bymodifying the intensity of the interaction among the interpenetratingpseudo-diamondoid frameworks using a dicarboxylic acid compoundrepresented by general formula (I) and a dipyridyl compound representedby general formula (II). More specifically, by putting a dicarboxylicacid compound having greater steric hindrance (to be referred to as“dicarboxylic acid compound B”) than the dicarboxylic acid compound thatcomposes the complex (to be referred to as “dicarboxylic acid compoundA”) into a solid solution with the metal complex serving as the base (inthe case of using one type of dicarboxylic acid compound), interactionamong pseudo-diamondoid frameworks weakens and the gate-opening pressureof the target adsorbate can be lowered. In this manner, gate-openingpressure for a target adsorbate can be lowered, allowing only the targetgas to be selectively adsorbed, by synthesizing using two or more typesof dicarboxylic acid compounds having different sizes.

In addition, in the present invention, adsorption rate can be controlledby modifying the ratio of gaps among the interpenetratingpseudo-diamondoid frameworks using a dicarboxylic acid compoundrepresented by general formula (I) and a dipyridyl compound representedby general formula (II). More specifically, by putting a dicarboxylicacid compound having less steric hindrance (to be referred to as“dicarboxylic acid compound B”) than the dicarboxylic acid compound thatcomposes the complex (to be referred to as “dicarboxylic acid compoundA”) into a solid solution with the metal complex serving as the base (inthe case of using one type of dicarboxylic acid compound), gaps formedamong the pseudo-diamondoid frameworks become larger and the diffusionrate of the target adsorbate in the pores can be increased. In thismanner, the gas adsorption rate can be improved and a more efficientseparation process can be designed by synthesizing using two or moretypes of dicarboxylic acid compounds having different sizes.

The aforementioned adsorption mechanism is only presumptive. Even in thecase the adsorption mechanism is not in accordance with that describedabove, it is encompassed in the scope of the present invention providedit satisfies the requirements provided for in the present invention.

<1,3-Butadiene Separation Method>

In the method of the present invention for separating 1,3-butadiene froma mixed gas containing 1,3-butadiene and hydrocarbons having four carbonatoms other than 1,3-butadiene, the mixed gas containing 1,3-butadieneas the separation target is contacted with the separating material ofthe present invention and the 1,3-butadiene is selectively adsorbed ontothe separating material, after which the 1,3-butadiene adsorbed to theseparating material is desorbed from the separating material and thereleased 1,3-butadiene is captured. The separating material isregenerated by desorption of the 1,3-butadiene.

Although there are no particular limitations on the hydrocarbon havingfour carbon atoms other than 1,3-butadiene contained in the mixed gas,the separating material of the present invention is particularlyeffective when separating 1,3-butadiene from a mixed gas containing asanother gas a hydrocarbon having four carbon atoms, such as butenesincluding isobutene, 1-butene, trans-2-butene and cis-2-butene, orbutanes including n-butane and isobutane, since it is difficult forconventional separating materials to separate these hydrocarbons from1,3-butadiene due to the proximity of their boiling points to that of1,3-butadiene.

Temperature and pressure conditions during contact between the mixed gasand separating material are preferably selected so that only the target1,3-butadiene is effectively adsorbed onto the separating material.

The separation method comprises an adsorption step for contacting amixed gas with the separating material of the present invention underconditions in which 1,3-butadiene is adsorbed onto the separatingmaterial. Conditions including adsorption pressure and adsorptiontemperature that enable the 1,3-butadiene to be adsorbed onto theseparating material can be suitably determined depending on such factorsas the apparatus design or required purity of the product gas. Forexample, the partial pressure of 1,3-butadiene in a mixed gas introducedinto the adsorption step is preferably 10 kPa to 200 kPa and morepreferably 30 kPa to 200 kPa. In addition, the adsorption temperature ispreferably −5° C. to 100° C. and more preferably 0° C. to 50° C.

The separation method can be pressure swing adsorption or temperatureswing adsorption.

In the case the separation method is pressure swing adsorption, theseparation method comprises a step for contacting a mixed gas containing1,3-butadiene with the separating material and making only the target1,3-butadiene to be selectively adsorbed onto the separating material(adsorption step), followed by a step for reducing the pressure to apressure that allows the 1,3-butadiene adsorbed to the separatingmaterial to be desorbed from the separating material (regenerationstep). The desorption pressure can be suitably determined depending onsuch factors as the apparatus design or production efficiency. Forexample, the desorption pressure is preferably 0.05 kPa to 30 kPa andmore preferably 0.05 kPa to 10 kPa.

The following provides a detailed explanation of pressure swingadsorption in the case the target gas is 1,3-butadiene with reference toFIG. 3. The separating material of the present invention is packed intoadsorption column AC1 and adsorption column AC2. A mixed gas (M)containing 1,3-butadiene, butene, butane and the like is pressurized toabout 0.3 MPa with a compressor and supplied from mixed gas storage tankMS to adsorption column AC1 packed with the separating material throughvalve V1 (to be abbreviated as “V1” and to apply similarly hereinafter).As can be understood from FIG. 7, if the partial pressure of1,3-butadiene exceeds 40 kPa, the 1,3-butadiene is selectively adsorbedonto the separating material within adsorption column AC1 (adsorptionstep). On the other hand, butanes and butenes are not adsorbed and aredischarged from adsorption column AC1. As a result, a concentratedbutane/butene gas (B) is sent to product storage tank PS2 through V7.Next, adsorption column AC1 is aerated by vacuum pump P1 with V1, V5, V6and V7 closed and V2 open. As can be understood from FIG. 7, when thepressure falls below 20 kPa, a gas (BD) consisting mainly of1,3-butadiene adsorbed to the separating material in adsorption columnAC1 is desorbed and sent to product storage tank PS1 (desorption step).An adsorption step is also similarly completed with respect toadsorption column AC2. After carrying out the desorption step ofadsorption column AC1 for a prescribed period of time, V1, V2, V3, V4,V7 and V8 are closed and V5 and V6 are opened and a residual mixed gasin adsorption column AC2 is recovered into adsorption column AC1 byutilizing the pressure difference between adsorption column AC1 andadsorption column AC2 (pressure equalization step). Each product gas canbe efficiently obtained without losing its purity by carrying out thispressure equalization step. Next, adsorption column AC2 is aerated byvacuum pump P1 with V2, V3, V5, V6 and V8 closed and V4 open, and a gas(BD) consisting mainly of 1,3-butadiene adsorbed at this time isdesorbed and sent to product storage tank PS1. A mixed gas (M)containing 1,3-butadiene is supplied to adsorption column AC1 with V2,V3, V5, V6 and V8 closed and V1 and V7 open after which the adsorptionstep is carried out again. The adsorption and desorption operations inadsorption columns AC1 and AC2 are alternately repeated in a cyclesuitably set with a timer and the like, resulting in continuousproduction of each product gas.

In the case the separation method is temperature swing adsorption, theseparation method comprises a step for contacting a mixed gas containing1,3-butadiene with the separating material and making only the target1,3-butadiene to be selectively adsorbed onto the separating material(adsorption step), followed by a step for raising the temperature to atemperature that allows the 1,3-butadiene adsorbed to the separatingmaterial to be desorbed from the separating material (regenerationstep). The desorption temperature can be suitably determined dependingon such factors as the apparatus design or production efficiency. Forexample, the desorption temperature is preferably −5° C. to 150° C. andmore preferably 20° C. to 100° C. The pressure is dependent on the rangeover which the temperature is allowed to swing, and a pressure from 0.1MPa to the pressure at which the raw material gas liquefies ispreferable.

In the case the separation method is pressure swing adsorption ortemperature swing adsorption, the step for contacting the mixed gas withthe separating material (adsorption step) and the step for changing thepressure or temperature to one at which 1,3-butadiene can be desorbedfrom the separating material (regeneration step) can be suitablyrepeated.

Membrane separation is another example of a separation method. Aseparation membrane can be obtained by disposing the metal complex onthe surface of a porous support by crystal growth, for example. Examplesof materials of the porous support that can be used preferably includealumina, silica, mullite, compositions composed of silica, alumina andother components, such as cordierite, porous sintered metals and porousglass. In addition, ceramics including other oxides, such as zirconia ormagnesia, carbides or nitrides, such as silicon carbide or siliconnitride, gypsum, cement or mixtures thereof can also be used. Theporosity of the porous support is typically about 30% to 80%, preferably35% to 70% and most preferably 40% to 60%. In the case porosity isexcessively low, the permeability of gases and other fluids decreases,thereby making this undesirable, while in the case porosity isexcessively high, the strength of the support ends up decreasing,thereby making this undesirable. In addition, the pore size of theporous support is typically 10 nm to 10,000 nm and preferably 100 nm to10,000 nm. A separation membrane having grown crystals of a metalcomplex on the surface of a porous support is obtained by immersing theporous support in a solution containing raw materials of the metalcomplex followed by heating as necessary.

In addition, a separation membrane can also be obtained by kneading themetal complex of the present invention with a polymeric material todisperse the metal complex in the polymeric material followed by forminginto a film. Examples of polymeric materials include polymeric materialsused for gas separation membranes, such as polyvinyl acetate, polyimideor polydimethylsiloxane.

In the case of membrane separation in which a mixed gas containing thetarget 1,3-butadiene is contacted with a separation membrane, thepermeability P of each gas in the mixed gas is expressed as the productof the solubility S of each gas in the membrane and the diffusioncoefficient D of each gas in the membrane. The higher the permeability Pof a gas, the greater the selectivity at which the gas passes throughthe membrane. Therefore, such a gas can be separated and recovered froma mixed gas. Accordingly, by forming the metal complex of the presentinvention, which is highly selective for 1,3-butadiene, into a membrane,the obtained membrane allows 1,3-butadiene to selectively pass through.For example, when a mixed gas is passed through an inner tube of adouble-walled tube provided with a gas-impermeable outer tube and theinner tube composed of a separation membrane, 1,3-butadiene selectivelypasses through the inner tube and is concentrated between the outer tubeand the inner tube. Therefore, the target 1,3-butadiene can beseparated.

Although the ratio of 1,3-butadiene in a mixed gas to be separated canbe varied, this ratio is greatly dependent on the supply source of themixed gas. In addition to 1,3-butadiene, a mixed gas may at leastcontain butenes, such as isobutene, 1-butene, trans-2-butene orcis-2-butene, and butanes, such as n-butane or isobutane as well asother hydrocarbons. The mixed gas preferably contains 10% by volume to99% by volume of 1,3-butadiene based on the total volumetric ratio of1,3-butadiene and other hydrocarbons (of which there may be multipletypes) present in the mixed gas. The ratio of 1,3-butadiene is morepreferably 20% by volume to 60% by volume.

The separating material of the present invention can be applied toseparation of fractions having four hydrocarbons (C4 fractions) obtainedby naphtha cracking. For example, after having pressurized a mixed gascontaining about 40% by volume of 1,3-butadiene to 150 kPa or higher,the mixed gas is passed through an adsorption column packed with theseparating material of the present invention for 1 minute to 10 minutes.Subsequently, after undergoing a pressure equalization step, thepressure is reduced to 20 kPa or lower with a vacuum pump, enabling the1,3-butadiene adsorbed to the separating material to be recovered.

EXAMPLES

Although the following provides a detailed explanation of the presentinvention through examples thereof, the present invention is not limitedto these examples. Analyses and evaluations in the following examplesand comparative examples were carried out in the manner described below.

(1) Measurement of Adsorption-Desorption Isotherms

Measurements were carried out by the volumetric method using ahigh-pressure gas adsorption apparatus. The samples were dried at 150°C. and 50 Pa for 6 hours prior to measurement to remove any adsorbedwater and the like. Details of the analysis conditions are indicatedbelow.

<Analysis Conditions>

Apparatus: BELSORP®-18HT manufactured by Bell Japan Inc. or BELSORP®-HPmanufactured by Bell Japan Inc.

Equilibration pause time: 500 seconds

(2) Measurement of Powder X-Ray Diffraction Patterns

X-ray diffraction patterns were measured according to a symmetricalreflection method at a scanning rate of 3°/minute over a diffractionangle range (2θ) of 3° to 50° using the MultiFlex X-ray diffractionsystem manufactured by Rigaku Corp. Mercury (ver. 2.3) available fromthe Cambridge Crystallographic Data Centre was used to convert singlecrystal structures to XRPD diffraction patterns.

Example 1 Synthesis of [Zn(NO₂ip)_(0.95)(tBuip)_(0.05)(bpe)]

Zinc oxide (0.41 g, 5.0 mmol, 1 eq.), 5-nitroisophthalic acid (1.00 g,4.8 mmol, 0.95 eq.), 5-tert-butylisophthalic acid (0.06 g, 0.3 mmol,0.05 eq.), 1,2-di(4-pyridyl)ethylene (0.92 g, 0.50 mmol, 1.0 eq.),distilled water (5 mL) and zirconia balls (diameter: 3 mm, 25 g) wereadded to a zirconia container (45 mL) followed by wet-grinding for 1hour at room temperature (25° C.) and 400 rpm (using the Classic LineP-7 manufactured by Fritsch Japan Co., Ltd.). Subsequently, the contentswere filtered using a Kiriyama® funnel, and the precipitated metalcomplex was washed with ion exchange water and ethanol in that order,followed by drying. 2.03 g (yield: 90%) of the metal complex wereobtained in the form of a white solid. The resulting metal complex wasconfirmed to be a metal complex having a structure that is a triplyinterpenetrating pseudo-diamondoid framework as shown in FIGS. 1 and 2by measurement of the powder X-ray diffraction pattern thereof. This wasdesignated as “Metal Complex 1”.

Examples 2 to 9 and Comparative Example 1

Metal Complexes 2 to 9 and Comparative Metal Complex 1 were produced inthe same manner as Example 1 with the exception of changing the reactionraw materials to the substances and amounts shown in Table 1.Comparative Metal Complex 1 used only one type of the dicarboxylic acidcompound (I).

Comparative Example 2

A typical zeolite adsorbent, Zeolite 13X (Union Showa K.K.), was used.

<Adsorption Isotherms>

The adsorption isotherms of 1,3-butadiene were measured at 25° C. forthe metal complexes of Examples 1 to 5 and Comparative Example 1. Theresults are shown in FIGS. 4 and 5. The metal complexes of Examples 1 to5, which contained two types of dicarboxylic acid compounds, began toadsorb 1,3-butadiene at a lower pressure than the complex of ComparativeExample 1. Accordingly, the complex of the present invention is clearlysuperior as a separating material of 1,3-butadiene.

<Adsorption Rates>

Time-based changes in adsorbed amounts were measured under theconditions of the initial pressure of 1,3-butadiene at 90 kPa and 25° C.for the metal complexes of Examples 6 to 9 and Comparative Example 1.The results are shown in FIG. 6, indicating that the metal complexes ofExamples 6 to 9, which contained two types of dicarboxylic acidcompounds, exhibited higher adsorption rates (adsorbed amount per unittime) than Comparative Example 1. Accordingly, the complex of thepresent invention is clearly superior as a separating material of1,3-butadiene.

<Adsorption-Desorption Isotherms>

The adsorption-desorption isotherms of 1,3-butadiene and trans-2-buteneat 25° C. were measured for Metal Complex 2 of Example 2 and the zeoliteof Comparative Example 2. The results are shown in FIG. 7 and FIG. 8,respectively.

FIG. 7 indicates that Metal Complex 2 of the present inventionselectively adsorbed 1,3-butadiene over a pressure range of 40 kPa to100 kPa. Thus, when a mixed gas composed of 1,3-butadiene andtrans-2-butene is contacted with Metal Complex 2 and the mixed gas issupplied at a partial pressure of 1,3-butadiene of 40 kPa or higher,only the 1,3-butadiene is selectively adsorbed. Next, since1,3-butadiene desorbs when the supply of mixed gas is halted and thepressure is lowered to 20 kPa or lower, a concentrated gas of1,3-butadiene can be obtained. On the other hand, FIG. 8 indicates that1,3-butadiene was not selectively adsorbed over a pressure range of 0kPa to 110 kPa. Namely, not only 1,3-butadiene, but also trans-2-butenealso ends up being adsorbed and 1,3-butadiene cannot be sufficientlyconcentrated.

TABLE 1 Dicarboxylic Dicarboxylic Metal Metal Raw Acid Acid DipytidylComplex Material Compound A Compound (B) Compound B/(A + B) Yield YieldNo. (g) (g) (g) (g) (mol %) (g) (%) Example 1 1 ZnO 0.41 5-NIP 1.005-BIP 0.06 DP-ethylene 0.92 5 2.03 90 Example 2 2 ZnO 0.41 5-NIP 0.955-BIP 0.12 DP-ethylene 0.91 10 1.98 87 Example 3 3 ZnO 0.41 5-NIP 0.845-BIP 0.23 DP-ethylene 0.92 20 1.96 83 Example 4 4 ZnO 0.41 5-NIP 0.965-SSIP 0.14 DP-ethylene 0.91 10 1.85 81 Example 5 5 ZnO 0.40 5-NIP 0.965-LSIP 0.13 DP-ethylene 0.91 10 1.89 83 Example 6 6 ZnO 0.41 5-NIP 0.95IP 0.08 DP-ethylene 0.91 10 1.98 87 Example 7 7 ZnO 0.41 5-NIP 0.955-MIP 0.09 DP-ethylene 0.91 10 1.97 87 Example 8 6 ZnO 0.40 5-NIP 0.95PDC 0.09 DP-ethylene 0.91 10 1.98 88 Example 9 9 ZnO 0.41 5-NIP 0.95 BTC0.10 DP-ethylene 0.91 10 1.16 51 Comp. Ex. 1 Comp. 1 ZnO 0.41 5-NIP 1.04None — DP-ethylene 0.91 0 1.88 82 5-NIP: 5-nitroisophthalic acid 5-BIP:5-tert-butylisophthalic acid 5-SSIP: Sodium 5-sulfoisophthalate 5-LSIP:Lithium 5-sulfoisophthalate IP: Isophthalic acid 5-MIP:5-methylisophthalic acid PDC: 3,5-pyridinedicarboxylic acid BTC:Trimesic acid DP-ethylene: 1,2-di(4-pyridyl)ethylene

BRIEF DESCRIPTION OF REFERENCE SYMBOLS

MS: Mixed gas storage tank

PS1, PS2: Product storage tanks

AC1, AC2: Adsorption columns

P1: Vacuum pump

V1 to V8: Valves

M: Mixed gas

B: Concentrated butane/butene gas

BD: Gas consisting mainly of 1,3-butadiene

The invention claimed is:
 1. A 1,3-butadiene separating material thatselectively adsorbs 1,3-butadiene from a mixed gas containing1,3-butadiene and a hydrocarbon having four carbon atoms other than1,3-butadiene, comprising a metal complex consisting of: a dicarboxylicacid compound (I) represented by the following general formula (I):

wherein X represents a carbon atom or nitrogen atom, Y represents ahydrogen atom, optionally substituted alkyl group having 1 to 4 carbonatoms, alkenyl group having 2 to 4 carbon atoms, alkoxy group having 1to 4 carbon atoms, formyl group, acyloxy group having 2 to 4 carbonatoms, hydroxyl group, alkoxycarbonyl group having 2 to 4 carbon atoms,nitro group, cyano group, amino group, monoalkylamino group having 1 to4 carbon atoms, dialkylamino group having 2 to 4 carbon atoms, acylaminogroup having 2 to 4 carbon atoms, sulfo group, sulfonate group, carboxylgroup or halogen atom in the case X represents a carbon atom or Y is notpresent in the case X represents a nitrogen atom, and R¹, R² and R³respectively and independently represent a hydrogen atom, optionallysubstituted alkyl group having 1 to 4 carbon atoms or halogen atom; anion of at least one type of metal selected from the group consisting ofberyllium, magnesium, calcium, strontium, barium, titanium, vanadium,chromium, manganese, iron, ruthenium, cobalt, rhodium, nickel,palladium, platinum, copper, zinc and cadmium; and a dipyridyl compound(II) represented by the following general formula (II):L-Z-L  (II) wherein L is represented by any of the following formulas:

wherein R⁴, R⁵, R⁶ and R⁷ respectively and independently represent ahydrogen atom, alkyl group having 1 to 4 carbon atoms or a halogen atom,and Z represents —CR8R9-CR10R11- (wherein R⁸, R⁹, R¹⁰and R¹¹respectively and independently represent a hydrogen atom, alkyl grouphaving 1 to 4 carbon atoms, hydroxyl group or halogen atom), an alkylenegroup having 3 to 4 carbon atoms, —CH═CH—, —C≡C—, —S—S—, —N═N—, —O—CH₂—,—NH—CH₂— or —NHCO—); wherein two or more different types of thedicarboxylic acid compound (I) are contained as the dicarboxylic acidcompound (I), wherein the dicarboxylic acid compound (I) comprises twoor more dicarboxylic acids selected from the group consisting ofisophthalic acid, 5-methylisophthalic acid 5-tert-butylisophthalic acid,5-methoxyisophthalic acid, 5-nitroisophthalic acid, sodium5-sulfoisophthalate, lithium 5-sulfoisphthalate and trimesic acid, andwherein the metal complex has a structure that is a triplyinterpenetrating pseudo-diamondoid framework.
 2. The 1,3-butadieneseparating material according to claim 1, wherein a combination of thedicarboxylic acid compounds (I) is 5-nitroisophthalic acid and sodium5-sulfoisophthalate, 5-nitroisophthalic acid and lithium5-sulfoisophthalate, or 5-nitroisophthalic acid and5-tert-butylisophthalic acid.
 3. The 1,3-butadiene separating materialaccording to claim 1, wherein the dipyridyl compound (II) is at leastone selected from the group consisting of 1,2-di(4-pyridyl)ethylene,1,2-di(4-pyridyl)ethane, 4,4′-azobispyridine and 4,4′-dipyridyldisulfide.
 4. The 1,3-butadiene separating material according to claim1, wherein the metal ion is at least one selected from the groupconsisting of a cobalt ion, nickel ion and zinc ion.
 5. The1,3-butadiene separating material according to claim 1, wherein thehydrocarbon having four carbon atoms other than 1,3-butadiene is atleast one selected from the group consisting of 1-butene, isobutene,trans-2-butene, cis-2-butene, isobutane and n-butane.
 6. A 1,3-butadieneseparation method comprising: an adsorption step for contacting aseparating material with a mixed gas containing 1,3-butadiene and ahydrocarbon having four carbon atoms other than 1,3-butadiene andselectively adsorbing 1,3-butadiene onto the separating material,followed by a regeneration step for desorbing the 1,3-butadiene adsorbedonto the separating material from the separating material and capturingthe released 1,3-butadiene, wherein the separating material comprises ametal complex consisting of: a dicarboxylic acid compound (I)represented by the following general formula (I):

wherein X represents a carbon atom or nitrogen atom, Y represents ahydrogen atom, optionally substituted alkyl group having 1 to 4 carbonatoms, alkenyl group having 2 to 4 carbon atoms, alkoxy group having 1to 4 carbon atoms, formyl group, acyloxy group having 2 to 4 carbonatoms, hydroxyl group, alkoxycarbonyl group having 2 to 4 carbon atoms,nitro group, cyano group amino group, monoalkylamino group having 1 to 4carbon atoms, dialkylamino group having 2 to 4 carbon atoms, acylaminogroup having 2 to 4 carbon atoms, sulfo group, sulfonate group, carboxylgroup or halogen atom in the case X represents a carbon atom or Y is notpresent in the case X represents a nitrogen atom, and R¹, R² and R³respectively and independently represent a hydrogen atom, optionallysubstituted alkyl group having 1 to 4 carbon atoms or halogen atom, anion of at least one type of metal selected from the group consisting ofberyllium, magnesium, calcium, strontium, barium, titanium, vanadium,chromium, manganese, iron, ruthenium, cobalt, rhodium, nickel,palladium, platinum, copper, zinc and cadmium; and a dipyridyl compound(II) represented by the following general formula (II)L-Z-L  (II) wherein L is represented by any of the following formulas:

wherein R⁴, R⁵, R⁶ and R⁷ respectively and independently represent ahydrogen atom, alkyl group having 1 to 4 carbon atoms or a halogen atom,and Z represents —CR⁸R⁹CR¹⁰R¹¹— (wherein R⁸, R⁹, R¹⁰, R¹¹ respectivelyand independently represent a hydrogen atom, alkyl group having 1 to 4carbon atoms, hydroxyl group or halogen atom), an alkylene group having3 to 4 carbon atoms, —CH═CH—, —C≡C—, —S—S—,—N═N—, —O—CH₂—, —NH—CH₂— or—NHCO—); wherein two or more different types of the dicarboxylic acidcompound (I) are contained as the dicarboxylic acid compound (I).
 7. The1,3-butadiene separation method according to claim 6, wherein theseparation method is pressure swing adsorption.
 8. The 1,3-butadieneseparation method according to claim 6, wherein the separation method istemperature swing adsorption.
 9. A 1,3-butadiene separation method,comprising: contacting a mixed gas containing 1,3-butadiene and ahydrocarbon having four carbon atoms other than 1,3-butadiene with aseparation membrane and selectively allowing the 1,3-butadiene to passthrough the separation membrane to obtain a gas having a higher1,3-butadiene concentration than the mixed gas, wherein the separationmembrane comprises a porous support and a 1,3-butadiene separatingmaterial attached to the surface of the porous support, wherein the1,3-butadiene separating material comprises a metal complex consistingof: a dicarboxylic acid compound (I) represented h the following generalformula (I);

wherein X represents a carbon atom or nitrogen atom, Y represents ahydrogen atom, optionally substituted alkyl group having 1 to 4 carbonatoms, alkenyl group having 2 to 4 carbon atoms, alkoxy group having 1to 4 carbon atoms, formyl group, acyloxy group having 2 to 4 carbonatoms, hydroxyl group, alkoxycarbonyl group having 2 to 4 carbon atoms,nitro group, cyano group, amino group, monalkylamino group having 1 to 4carbon atoms, dialkylamino group having 2 to 4 carbon atoms, acylaminogroup having 2 to 4 carbon atoms, sulfo group, sulfonate group, carboxylgroup or halogen atom in the case X represents a carbon atom or Y is notpresent in the case X represents a nitrogen atom, and R¹, R² and R³respectively and independently represent a hydrogen atom, optionallysubstituted alkyl group having 1 to 4 carbon atoms or halogen atom; anion of at least one type of metal selected from the group consisting ofberyllium, magnesium, calcium, strontium, barium, titanium, vanadium,chromium, manganese, iron, ruthenium, cobalt, rhodium, nickel,palladium, platinum, copper, zinc, and cadmium; and a dipyridyl compound(II) represented by the following general formula (II):L-Z-L  (II) wherein L is represented by any of the following formulas:

wherein R⁴, R⁵, R⁶ and R⁷ respectively and independently represent ahydrogen atom, alkyl group having 1 to 4 carbon atoms or halogen atom,and Z represent —CR⁸R⁹—CR¹⁰R¹¹— (wherein R⁸, R⁹, R¹⁰ and R¹¹respectively and independently represent a hydrogen atom, alkyl grouphaving 1 to 4 carbon atoms, hydroxyl group or halogen atom), an alkylenegroup having 3 to 4 carbon atoms, —CH═CH—, —C≡C—, —S—S—, —N═N—, —O—CH₂—,—NH—CH₂— or —NHCO—); wherein two or more different types of thedicarboxylic acid compound (I) are contained as the dicarboxylic acidcompound (I).
 10. A method for producing a metal complex consisting of:a dicarboxylic acid compound (I) represented by the following generalformula (I):

wherein X represents a carbon atom or nitrogen atom, Y represents ahydrogen atom, optionally substituted alkyl group having 1 to 4 carbonatoms, alkenyl group having 2 to 4 carbon atoms, alkoxy group having 1to 4 carbon atoms, formyl group, acyloxy group having 2 to 4 carbonatoms, hydroxyl group, alkoxycarbonyl group having 2 to 4 carbon atoms,nitro group, cyano group, amino group, monoalkylamino group having 1 to4 carbon atoms, dialkylamino group having 2 to 4 carbon atoms, acylaminogroup having 2 to 4 carbon atoms, sulfo group, sulfonate group, carboxylgroup or halogen atom in the case X represents a carbon atom or Y is notpresent in the case X represents a nitrogen atom, and R¹, R² and R³respectively and independently represent a hydrogen atom, optionallysubstituted alkyl group having 1 to 4 carbon atoms or halogen atom; anion of at least one type of metal selected from the group consisting ofberyllium, magnesium, calcium, strontium, barium, titanium, vanadium,chromium, manganese, iron, ruthenium, cobalt, rhodium, nickel,palladium, platinum, copper, zinc, and cadmium; and a dipyridyl compound(II) represented by the following general formula (II):L-Z-L  (II) wherein L is represented by any of the following formulas:

wherein R⁴, R⁵, R⁶ and R⁷ respectively and independently represent ahydrogen atom, alkyl group having 1 to 4 carbon atoms or halogen atom,and Z representes —CR⁸R⁹—CR¹⁰R¹¹— (wherein R⁸, R⁹, R¹⁰, and R¹¹respectively and independently represent a hydrogen atom, alkyl grouphaving 1 to 4 carbon atoms, hydroxyl group or halogen atom), an alkylenegroup having 3 to 4 carbon atoms, —CH═CH—, —C≡C—, —S—S—, —N═N—, —O—CH₂—,—NH—CH₂— or —NHCO—); wherein two or more different types of thedicarboxylic acid compound (I) are contained as the dicarboxylic acidcompound (I), the method comprising reacting a salt of at least one typeof metal selected from the group consisting of beryllium, magnesium,calcium, strontium, barium, titanium, vanadium, chromium, manganese,iron, ruthenium, cobalt, rhodium, nickel, palladium, platinum, copper,zinc and cadmium, two or more types of the dicarboxylic acid compound(I), and the dipyridyl compound (II) and precipitating a metal complex,wherein wet grinding is carried out during the reaction.
 11. The1,3-butadiene separation method according to claim 6, wherein thedicarboxylic acid compound (I) comprises two or more dicarboxylic acidsselected from the group consisting of isophthalic acid,5-methylisophthalic acid, 5-tert-butylisophthalic acid,5-methoxyisophthalic acid, 5-nitroisophthalic acid, sodium5-sulfoisophthalate, lithium 5-sulfoisophthalate and trimesic acid. 12.The 1,3-butadiene separation method according to claim 6, wherein acombination of the dicarboxylic acid compounds (I) is 5-nitroisophthalicacid and sodium 5-sulfoisophthalate, 5-nitroisophthalic acid and lithium5-sulfoisophthalate, or 5-nitroisophthalic acid and5-tert-butylisophthalic acid.
 13. The 1,3-butadiene separation methodaccording to claim 6, wherein the dipyridyl compound (II) is at leastone selected from the group consisting of 1,2-di(4-pyridyl)ethylene,1,2-di(4-pyridyl)ethane, 4,4′-azobispyridine and 4,4′-dipyridyldisulfide.
 14. The 1,3-butadiene separation method according to claim 6,wherein the metal ion is at least one selected from the group consistingof a cobalt ion, nickel ion and zinc ion.
 15. The 1,3-butadieneseparation method according to claim 6, wherein the metal complex has astructure that is a triply interpenetrating pseudo-diamondoid framework.